[Todos] Coloquios del Departamento de Física (jueves 14/4)

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Recordamos el coloquio de hoy,



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                         COLOQUIOS DEL DEPARTAMENTO DE FÍSICA FCEyN - UBA

                                  http://coloquios.df.uba.ar/

                                   Charla, café y galletitas
                         En el Aula Federman, 1er piso, Pabellón I,
                                       Ciudad Universitaria


                               Jueves 14 de abril, 14 hs


                       Metodologia sismica para monitorear
                        el secuestro de CO2 en el subsuelo


                                  José M. Carcione

                          Istituto Nazionale di Oceanografia e
                             di Geofisica Sperimentale
                                  Trieste, Italia.

The main anthropic cause of climate change is the release of carbon
dioxide (CO2) into the atmosphere. Fossil-fuel combustion generates in
excess 27 billion tons of CO2 per year. There is evidence that this
concentration of CO2 has increased the atmosphere temperature by
0.3-0.6 oC during the last 150 years. To solve this problem,
geological sequestration is an immediate option. The possibilities are
injection into hydrocarbon reservoirs, methane-bearing coal beds and
saline aquifers. An example of the latter is the Sleipner field in the
North Sea, where CO2 is stored in the Utsira formation, a highly
permeable porous sandstone 800 m below the sea bottom. Carbon dioxide
stored in saline aquifers has some advantages, because it does not require
structural and stratigraphic trap geometries. The storage can be  
hydrodynamic as
dissolved CO2 in the formation waters. However, the disposal should be
made at supercritical pressures to avoid the presence of the gas
phase, with the minimum aquifer depth of nearly 1 km (the critical
pressure and temperature of CO2 are 7.4 MPa and 31 oC, respectively)
(1 MPa = 10 bar = 145.04 psi = 9.87 atm.).
We present a new petro-elastical model and seismic monitoring
methodology for reservoirs subject to CO2 sequestration. The
petro-elastical equations model the seismic properties of reservoir
rocks  saturated with CO2, methane, oil and brine. The gas properties
are obtained from the van der Waals equations and we take into account
the absorption of gas by oil and brine as a function of the in-situ
pore pressure and temperature. The dry-rock bulk and shear moduli can
be obtained either by calibration from real data or by using
rock-physics models based on the Hertz-Mindlin and Hashin-Shtrikman
theories. Mesoscopic attenuation due to fluids effects is quantified  
by using White's model of patchy saturation, and the wet-rock  
velocitiesare calculated with Gassmann equations by using an effective  
fluid modulus to describe the
velocities predicted by White's model. Synthetic seismograms are
computed with a poro-viscoelastic modeling code based on Biot's
theory, where viscoelasticity is described by generalizing the
solid/fluid coupling modulus to a relaxation function. Using the
pseudospectral method, which allows general material variability, a
complete and accurate characterization of the reservoir can be
obtained. Two cases consider the Utsira sand of the North Sea and the
Atzbach-Schwanenstadt gas field in Upper Austria. The monitoring
approach involves traveltime reflection tomography
and rock physics; the synthetic seismograms can be used to test the
sensitivity of the methodology.